[dpdk-dev] [PATCH v5 1/3] rcu: add RCU library supporting QSBR mechanism

[Ananyev, Konstantin]

> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen at networkplumber.org]
> Sent: Saturday, April 13, 2019 12:06 AM
> To: Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>
> Cc: Ananyev, Konstantin <konstantin.ananyev at intel.com>; paulmck at linux.ibm.com; Kovacevic, Marko <marko.kovacevic at intel.com>;
> dev at dpdk.org; Gavin Hu (Arm Technology China) <Gavin.Hu at arm.com>; Dharmik Thakkar <Dharmik.Thakkar at arm.com>; Malvika Gupta
> <Malvika.Gupta at arm.com>; nd <nd at arm.com>
> Subject: Re: [PATCH v5 1/3] rcu: add RCU library supporting QSBR mechanism
> 
> On Fri, 12 Apr 2019 22:24:45 +0000
> Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com> wrote:
> 
> > >
> > > On Fri, 12 Apr 2019 15:20:37 -0500
> > > Honnappa Nagarahalli <honnappa.nagarahalli at arm.com> wrote:
> > >
> > > > Add RCU library supporting quiescent state based memory reclamation
> > > method.
> > > > This library helps identify the quiescent state of the reader threads
> > > > so that the writers can free the memory associated with the lock less
> > > > data structures.
> > > >
> > > > Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
> > > > Reviewed-by: Steve Capper <steve.capper at arm.com>
> > > > Reviewed-by: Gavin Hu <gavin.hu at arm.com>
> > > > Reviewed-by: Ola Liljedahl <ola.liljedahl at arm.com>
> > > > Acked-by: Konstantin Ananyev <konstantin.ananyev at intel.com>
> > >
> > > After evaluating long term API/ABI issues, I think you need to get rid of almost
> > > all use of inline and visible structures. Yes it might be marginally slower, but
> > > you thank me the first time you have to fix something.
> > >
> > Agree, I was planning on another version to address this (I am yet to take a look at your patch addressing the ABI).
> > The structure visibility definitely needs to be addressed.
> > For the inline functions, is the plan to convert all the inline functions in DPDK? If yes, I think we need to consider the performance
> difference. May be consider L3-fwd application, change all the inline functions in its path and run a test?
> 
> Every function that is not in the direct datapath should not be inline.
> Exceptions or things like rx/tx burst, ring enqueue/dequeue, and packet alloc/free

Plus synchronization routines: spin/rwlock/barrier, etc.
I think rcu should be one of such exceptions - it is just another synchronization mechanism after all
(just a bit more sophisticated).
Konstantin